adding tooltips to google visualization bar chart

I'm trying to add custom tooltips to a Google Bar Chart, but I can't figure out how to do this. Google provides a nice tutorial (at https://developers.google.com/chart/interactive/docs/customizing_tooltip_content), but it only discusses ColumnCharts, rather than Bar Charts.

Here's what my code looks like:

<div id="top_x_div" style="width: 900px; height: 500px;"></div>

google.load("visualization", "1.1",{packages:["bar"]});
google.setOnLoadCallback(drawStuff0);

function drawStuff0() {
   var data = new google.visualization.arrayToDataTable([$data]);
   var options = {
       title: 'Categories',
       width: 900,
       legend: { position: 'none' },
       chart: { title: 'popularity by number of queries',
                subtitle: 'Number of times a category was queried' },
       bars: 'horizontal', // Required for Material Bar Charts.
       axes: {
                x: {
                    0: { side: 'top', label: 'Number of times a category was queried'} // Top x-axis.
                }
             },
       bar: { groupWidth: "90%" }
   };

   var chart = new google.charts.Bar(document.getElementById('top_x_div0'));

   // Convert the Classic options to Material options.
   chart.draw(data, google.charts.Bar.convertOptions(options));
};

$data is simply a PHP variable containing the rows of the chart.

Could someone explain how to add a custom tooltip to this chart? I've looked all over the web for a solution, I haven't been able to find one...

Add a new column to the DataTable object with the role tooltip :

data.addColumn({type: 'string', role: 'tooltip'});

Then loop through data and add whatever tooltip you want (example from the one column bar chart fiddle below) for each row :

for (var i=0; i<data.getNumberOfRows(); i++) {
   data.setValue(i, 2, 'Tooltip #'+i);
}

demo -> http://jsfiddle.net/pc3zmb8w/

I cannot guide you more exactly since we dont know what your PHP $data is or how your chart looks like. But this is basically how you should do it, in all cases, when you want to add custom tooltips to a chart dynamically ...

Update - styling the tooltip

As for "is there a way to have the tool-tips appear as a rectangle, rather than a speech blurb", in the options - set tooltip as isHtml :

var options = {
    tooltip: {isHtml: true} 
}

Then the tooltip appears as a rectangle like normal HTML-element tooltips. You can also specify that you want to use HTML inside the tooltip itself :

data.addColumn({type: 'string', role: 'tooltip', p: {'html': true}});

For example to show the tooltip with the colors of a normal tooltip, but using a larger fontsize and a certain font :

div.tooltip {
    background-color: #ffffca;
    color: #000023;
    padding: 10px;
    font-size: 20px;
    font-family : 'arial';
}

Set the tooltip as in original answer :

data.setValue(i, 2, '<div class="tooltip">Tooltip #'+i+'</div>');

function drawChart() {
  var data = google.visualization.arrayToDataTable([
    ['x', 'Cats'],
    ['A', 1],
    ['B', 2],
    ['C', 4],
    ['D', 8],
    ['E', 7],
    ['F', 7],
    ['G', 8],
    ['H', 4]
  ]);

  data.addColumn({
    type: 'string',
    role: 'tooltip',
    p: {
      'html': true
    }
  });
  for (var i = 0; i < data.getNumberOfRows(); i++) {
    data.setValue(i, 2, '<div class="tooltip">Tooltip #' + i + '</div>');
  }

  var options = {
    title: 'Test chart',
    tooltip: {
      isHtml: true
    }
  };

  var chart = new google.visualization.BarChart(document.getElementById('chart'));
  chart.draw(data, options);

}

google.load("visualization", "1", {
  packages: ["corechart"]
});
google.setOnLoadCallback(drawChart);

#chart {
  width: 500px;
  height: 500px;
}

div.tooltip {
  background-color: #ffffca;
  color: #000023;
  padding: 10px;
  font-size: 20px;
  font-family: 'arial';
}

<script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
<div id="chart"></div>